SELF-REGULATING DAMPER. 



of the column of water sustained in the feed pipe. This column, 

 therefore, necessarily rises and falls with every variation in the 

 rate of evaporation in the boiler. A hollow float P is placed upon 

 the surface of the water of this column ; a chain connected with 

 this float is carried upwards, and passed over two pulleys, after 

 which it is carried downwards through an aperture leading to the 

 flue which passes beside the boiler : to this chain is attached the 

 damper. By such an arrangement it is evident that the damper will 

 rise when the float P falls, and will fall when the float P rises, since 

 the weight of the damper is so adjusted, that it will only balance 

 the float P when the latter rests on the surface of the water. 



"Whenever the evaporation of the boiler is insuflicient, it is 

 evident from what has been stated, that the float P will fall and 

 the damper will rise, and will afford a greater passage for air 

 through the flue. This will stimulate the furnace, will augment 

 its heating power, and will therefore increase the rate of evapo- 

 ration in the boiler. If, on the other hand, the production of 

 steam in the boiler be more than is requisite for the supply of the 

 engine, the float will be raised and the damper let down, so as to 

 contract the flue, N to diminish the draught, to mitigate the fire, 

 and therefore to check the evaporation. In this way the excess, 

 or defect, of evaporation in the boiler is made to act upon the fire, 

 so as to render the heat proceeding from the combustion as nearly 

 as possible proportional to the wants of the engine. 



18. Having thus explained generally the principal expedients 

 by which the efficiency of the boiler and furnace of a steam-engine 

 is maintained, it will be only necessary to add, that although 

 these expedients, in the forms in which they are represented in 

 the diagrams, will not be found in every steam boiler, yet equi- 

 valents to them in other forms or positions are almost universal. 

 In certain cases the self-regulating apparatus of the boiler and 

 furnace are excluded by want of the necessary height, and then 

 the proper regulation of the machine must depend on the skill and 

 vigilance of those who are in charge of it. 



Supposing, then, that by these or other similar or equivalent 

 provisions a supply of steam in the necessary quantity and of the 

 requisite pressure is obtained, it remains to show how the steam is 

 made to produce the desired mechanical effect. 



The method universally adopted to render the power of steam 

 available for mechanical purposes is that of a solid piston moving 

 freely in a hollow cylinder in steam-tight contact with its sides. 

 The steam is admitted alternately at one end and at the other, of 

 the cylinder. When it is let in at either end, it is permitted to 

 escape by the other, so that the piston is blown by the steam 

 alternately from end to end of the cylinder. The ends of the 



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